Multilayer wiring board assembly, multilayer wiring board assembly component and method of manufacture thereof

ABSTRACT

A multilayer wiring board assembly, a multilayer wiring board assembly component, and a method of manufacture thereof. The multilayer wiring board assembly is formed by laminating together a plurality of multilayer wiring board assembly components, having a flexible resin film with a copper foil bonded to one surface and an adhesive layer bonded to the other surface, opening a through hole in the copper plated resin film through the copper foil, resin film, and the adhesive layer, and filling the through hole with a conductive paste projecting from the adhesive layer and laterally extending beyond through hole opening of the copper foil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Applications P2001-85224 filed on Mar. 23, 2001; P2002-76334 filed on Mar. 19, 2002; P2002-76335 filed on Mar. 19, 2002; P2002-76226 filed on Mar. 19, 2002; P2002-76523 filed on Mar. 19, 2002; the entire contents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer wiring board assembly composed of a plurality of printed circuit boards in a multilayered structure, a multilayer wiring board assembly component for use in laminating the same and the manufacturing method of the same. In particular, the present invention relates to a multilayer wiring board assembly, a multilayer wiring board assembly component for use in laminating the same and the manufacturing method of the same, wherein the multilayer wiring board assembly is flexible and implemented with a highly packing density by the Flip Chip Mounting technique and so forth.

2. Description of the Related Art

A flexible printed circuit board (which is simply referred to as an “FPC” in this description) is composed of a resin film having a small thickness for the purpose of maintaining the flexibility thereof. Because of this, in the case of such FPCs, it is essentially very difficult to assemble a plurality of FPCs in a multilayered structure (a multilayer wiring board assembly). However, along with the advent of the implementation of FPCs with a highly packing density, the need for multilayered structures of FPCs has increased in recent years, for example, in consideration of the arrangement of lead wirings as connected to flip chips mounted on FPCs. In this situation, a multilayer wiring board assembly has been manufactured by multilayering a plurality of FPCs with an intervening glass epoxy prepreg sheet and so forth between each adjacent boards while one or both surface of each FPC has been formed with a circuit pattern, forming holes through the entirety of all the layers by means of a drill and the like, and interlayer interconnecting the layers by the use of a through hall plating and the like.

However, in the case of such a conventional method of manufacturing multilayer wiring board assemblies by the use of a through hall plating, it is impossible to form a via hole anew on another via hole and to mount a chip on a via hole, generally called as via-on-via since a hole remains in the center of a through hall even after plating. Because of this, when a multilayer wiring board assembly is implemented with a highly packing density, there are several impediments such that a lead can not be extended from the position just below the chip while interlayer interconnection tends to excessively occupy a substantial area.

On the other hand, for example, ALIVH (Any Layer Interstitial Via Hole: a registered trademark of Matsushita Electric Industrial Co., Ltd.) is a rigid multilayer wiring board assembly in which via-on-via is possible while a conductive paste is used for interlayer interconnection between each adjacent layers. An ALIVH board is formed by repeating the process sequence including opening a through hole in an uncured resin board, filling the through hole with a conductive paste, joining a copper foil to the uncured resin board, hardening the resin while compression bonding in order to form a multilayered structure and etching the copper foil in order to form a circuit pattern.

However, while via-on-via is possible in the case of the manufacturing method as described above to form ALIVH boards since the interlayer interconnection is made by means of a conductive paste, it is extremely difficult to manufacture FPCs in the form of a multilayer wiring board assembly by applying the manufacturing method to FPCs because it is necessary to open a hole through a resin film such as a polyimide film having a small thickness followed by filling up the hole with a conductive paste. This is because, when opening a hole in a resin film having a small thickness, the position and the size of the hole tend to change due to distortion of the resin film, the sucking force of a drill and the like so that the necessary accuracy of alignment is hardly achieved during the printing operation of the conductive paste and the positioning of the respective layers.

Also, while via-on-via is possible in the case of the manufacturing method making use of a conductive paste for the interlayer interconnection like ALIVH, it is difficult to make electric connection between a copper foil and a conductive paste without compromising the electric characteristics of the copper foil and the conductive paste so that the respective venders make use of proprietary methods respectively. Namely, generally speaking, when interlayer interconnection is made by via-on-via, a copper foil and a conductive paste are connected to each other by inserting the copper foil between adjacent conductive paste layers. In this case, the conductive paste is arranged to pierce the copper foil for the purpose of preserving electric connectivity between the copper foil and the conductive paste filler. For example, in the case of an ALIVH board, a conductive paste is printed in order to form a projection while the thickness of the board is reduced during thermocompression for bonding because of the use of an uncured resin board so that it becomes possible to make electric connection of a copper foil pierced by the projection of the conductive paste.

However, in the case of a board made of such a substance that the thickness of the board is not reduced during thermocompression for bonding, like a polyimide used for making a resin film in the case of FPCs, the projection of a conductive paste is less effective in piecing the copper foil. As a result, it is difficult to make electric connection between a copper foil and a conductive paste without compromising the electric characteristics.

Furthermore, in the case where a through hole is filled with a conductive paste, the conductive paste is printed in the condition that the surface of the conductive paste is slightly depressed since the conductive paste is pressed during printing. Because of this, there is a problem that, even if boards having through holes filled with a conductive paste are joined to each other, it is impossible to achieve sufficient electric connectivity between the fillers of the conductive paste.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in order to solve the shortcomings as described above. It is an object of the present invention to provide a multilayer wiring board assembly, a multilayer wiring board assembly component and a method of manufacture thereof in which it is possible to easily laminate together flexible FPCs having highly packing densities by via-on-via and chip-on-via.

It is another object of the present invention to provide a multilayer wiring board assembly which can be manufactured by joining multilayer wiring board assembly components to each other with a uniform pressure and therefore it is possible to fixedly laminate the multilayer wiring board assembly with a better electric connectivity.

It is a further object of the present invention to provide a multilayer wiring board assembly which is manufactured in order that the opening of a through hole near a copper foil is placed on a plane table having a hole of a diameter larger than that of the through hole followed by filling the through hole with a conductive paste from a masking tape in order to form a brim laterally extending beyond the perimeter of the opening of the copper foil, and therefore it is possible to form the brim having a desired profile with a high degree of accuracy and having a smaller thickness than that in the case utilzing a mask, and therefore possible to fixedly laminate the multilayer wiring board assembly with a better electric connectivity.

It is a still further object of the present invention to provide a multilayer wiring board assembly in which the contact area of a conductive paste filler with a copper foil is increased when compression bonding multilayer wiring board assembly components to each other, and therefore it is possible to improve electric connectivity.

It is a still further object of the present invention to provide a multilayer wiring board assembly in which it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property with little damage to the respective boards during the manufacturing process by the use of an adhesive layer made of a thermosetting resin.

It is a still further object of the present invention to provide a multilayer wiring board assembly in which it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property without damaging the conductive resin components (the conductive paste) by the use of an adhesive layer formed of a thermoplastic resin to which is given a thermosetting property.

In accordance with an aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded by screen printing in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with another aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of forming a through hole in a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which said through hole is opened through said copper foil, said resin film and said adhesive layer; and a step of embedding a conductive paste filler by screen printing in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of etching a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof in order to form a predetermined circuit pattern; a step of forming a mask layer on said adhesive layer of the copper plated resin film having been formed with said circuit pattern; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said mask layer; a step of embedding a conductive paste filler by screen printing in the through hole of said copper plated resin film from said copper foil; and a step of removing said mask layer.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly component and a multilayer wiring board in accordance with the present invention, a through hole is opened through the copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface, and filled with a conductive paste, and therefore it becomes easy to form the through hole and embed the conductive paste because of the increase in thickness as compared with the case where a through hole is opened only through a resin film and filled with a conductive paste. In this case, it is possible to improve electric connectivity between the copper foil and the conductive paste filler by embedding the through hole in order that the conductive paste filler is laterally extending beyond the perimeter of the opening of the through hole.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is laminated with a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above in which the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with the copper foil or the conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is manufactured by laminating together a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein said multilayer wiring board assembly is laminated with a plurality of said multilayer wiring board assembly components through said adhesive layer in order that the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

Namely, in the case of the multilayer wiring board assembly and the manufacturing method thereof in accordance with the present invention, the conductive paste filler of the multilayer wiring board assembly component is embedded in the through hole of the copper plated resin film by screen printing with a leading end of the conductive paste filler being projected from the adhesive layer, and therefore it is possible to make reliable electric connection of the leading end of the conductive paste filler with the copper foil or the conductive paste filler of the multilayer wiring board assembly component and to improve electric connectivity between the respective layers when a plurality of the multilayer wiring board assembly components are laminated together. Particularly, in this case, direct connection between the conductive paste fillers without the intermediary copper foil is effective to improve the electric connectivity.

Meanwhile, the adhesive layer can be made of, for example, a thermoplastic adhesive. In this case, the respective adjacent multilayer wiring board assembly components are fixedly joined by means of the adhesive layer which is made soft by laminating the multilayer wiring board assembly components together and heating them, and therefore it is possible to make reliable electric connection of the conductive paste filler with the copper foil and the conductive paste filler of the adjacent multilayer wiring board assembly component. Also, in this case, smooth electrical connection can be achieved by finally curing the conductive paste filler at the same time as the multilayer wiring board assembly components are laminated together.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of forming a through hole in a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which said through hole is opened through said copper foil, said resin film and said adhesive layer; and a step of embedding a conductive paste filler in the through hole from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film with one end of said conductive paste filler being projected from said adhesive layer and the tail end of said conductive paste filler being projected to the same height as said copper foil.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer and with part of said conductive paste being laterally extending beyond the perimeter of the opening of the through hole of said copper foil.

In accordance with a further aspect of the present invention, a multilayer wiring board assembly comprises: a first multilayer wiring board assembly component comprising a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer, and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer and with part of said conductive paste being laterally extending beyond the perimeter of the opening of the through hole of said copper foil; and a second multilayer wiring board assembly component comprising a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer, and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer and the tail end of said conductive paste filler being projected to the same height as said copper foil,

wherein said second multilayer wiring board assembly component is located as the most outer layer of the multilayer wiring board assembly while said first multilayer wiring board assembly component is located as an inner layer of the multilayer wiring board assembly other than said second multilayer wiring board assembly, and wherein the leading end of said conductive paste filler of one of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, the multilayer wiring board assembly is manufactured as described above and in order that said second multilayer wiring board assembly component is located as the most outer layer of the multilayer wiring board assembly while said first multilayer wiring board assembly component is located as an inner layer of the multilayer wiring board assembly other than said second multilayer wiring board assembly, and wherein wherein said multilayer wiring board assembly is laminated with a plurality of said multilayer wiring board assembly components through said adhesive layer in order that the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly component and a multilayer wiring board in accordance with the present invention, the upper surface of the most outer layer (most upper layer) is formed in order that the upper surface of the copper foil and the leading end of the conductive paste filler, i.e., the printing surface, are arranged to form a continuous flat surface having the same height so that it is possible to apply a uniform pressure to the entirety of the multilayer wiring board assembly during lamination.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of etching a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof in order to form a predetermined circuit pattern; a step of forming a mask layer on said adhesive layer of the copper plated resin film having been formed with said circuit pattern; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said mask layer; a step of placing, on said copper foil over said through hole, a mask of a thickness larger than that of said through hole; a step of embedding a conductive paste filler in said through hole with the tail end of said conductive paste filler being located at the same height as said mask; a step of removing said mask to leave said tail end of said conductive paste filler being projected from said copper foil with part of said conductive paste being laterally extending beyond the perimeter of the opening of the through hole of said copper foil; and a step of removing said mask to leave the tail end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises:a step of etching a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof in order to form a predetermined circuit pattern; a step of forming a mask layer on said adhesive layer of the copper plated resin film having been formed with said circuit pattern; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said mask layer; a step of placing said copper plated resin film on a plane table in which a hole is opened with a thickness larger than that of said through hole in order that said copper foil is located in a lower position with the through hole located over the hole of said plane table; a step of embedding a conductive paste filler in the through hole of said copper plated resin film from said mask layer with a leading end of said conductive paste filler being projected from said copper foil with part of said conductive paste being laterally extending beyond the perimeter of the opening of the through hole of said copper foil; and a step of removing said mask layer to leave the tail end of said conductive paste filler being projected from said adhesive layer.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly component in accordance with the present invention, the opening of a through hole near a copper foil is placed on a plane table having a hole of a diameter larger than that of the through hole followed by filling the through hole with a conductive paste from a masking tape in order to form a brim laterally extending beyond the perimeter of the opening of the copper foil, and therefore it is possible to form the brim having a desired profile with a high degree of accuracy and having a smaller thickness than that in the case utilzing a mask. By this configuration, the multilayer wiring board assembly is fixedly laminated with a better electric connectivity.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer and with the tail end of said conductive paste filler being projected from said copper foil.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is manufactured by laminating with a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein said multilayer wiring board assembly is laminated with a plurality of said multilayer wiring board assembly components through said adhesive layer in order that the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of preparing a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface thereof and forming first and second mask layers on said one surface and said other surface of said copper plated resin film; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said first and second mask layers; a step of embedding a conductive paste filler in said through hole with the leading and tail ends of said conductive paste filler being located at the same height as said mask layers; and a step of removing said first and second mask layers to leave the leading end of said conductive paste filler being projected from said adhesive layer with the tail end of said conductive paste filler being projected from said copper foil.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly component and a multilayer wiring board in accordance with the present invention, since the leading end of the conductive paste filler is projected from the adhesive layer while the tail end of said conductive paste filler is projected from said copper foil, the multilayer wiring board assembly is fixedly laminated with a better electric connectivity.

In accordance with a still further aspect of the present invention, multilayer wiring board assembly component comprises: a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermosetting resin and bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of forming a through hole in a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermosetting resin and bonded to the other surface thereof and in which said through hole is opened through said copper foil, said resin film and said adhesive layer; and a step of embedding a conductive paste filler in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of etching a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermosetting resin and bonded to the other surface thereof in order to form a predetermined circuit pattern; a step of forming a mask layer on said adhesive layer of the copper plated resin film having been formed with said circuit pattern; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said mask layer; a step of embedding a conductive paste filler in the through hole of said copper plated resin film from said copper foil; and a step of removing said mask layer.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is laminated with a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is manufactured by laminating together a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein said multilayer wiring board assembly is laminated through said adhesive layer in order that the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly component and a multilayer wiring board in accordance with the present invention, it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property with little damage to the respective boards during the manufacturing process.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly component comprises: a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermosetting resin to which is given a thermosetting property and bonded to the other surface thereof and in which a through hole is opened through said copper foil, said resin film and said adhesive layer; and a conductive paste filler embedded in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of forming a through hole in a copper plated resin film made of a resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermoplastic resin to which is given a thermosetting property and bonded to the other surface thereof and in which said through hole is opened through said copper foil, said resin film and said adhesive layer; and a step of embedding a conductive paste filler in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said adhesive layer.

In accordance with a still further aspect of the present invention, a manufacturing method of a multilayer wiring board assembly component comprises: a step of etching a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer made of a thermoplastic resin to which is given a thermosetting property and bonded to the other surface thereof in order to form a predetermined circuit pattern; a step of forming a mask layer on said adhesive layer of the copper plated resin film having been formed with said circuit pattern; a step of forming a through hole opened through said copper foil, said resin film, said adhesive layer and said mask layer; a step of embedding a conductive paste filler by screen printing in the through hole of said copper plated resin film from said copper foil; and a step of removing said mask layer.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly laminated a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein the leading end of said conductive paste filler of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, a multilayer wiring board assembly is manufactured by laminating together a plurality of multilayer wiring board assembly components including the multilayer wiring board assembly component as described above wherein said multilayer wiring board assembly is laminated with said adhesive layer in order that said leading end of said conductive paste filler of said at least one of said multilayer wiring board assembly components makes electric contact with said copper foil or said conductive paste filler of an adjacent one of said multilayer wiring board assembly components.

Namely, in the case of the manufacturing method of a multilayer wiring board assembly and a multilayer wiring board component in accordance with the present invention, by the use of an adhesive layer is formed of a thermoplastic resin to which is given a thermosetting property, and therefore it is possible to provide a multilayer wiring board assembly in which it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property without damaging the conductive resin components (the conductive paste).

BRIEF DESCRIPTION OF DRAWINGS

The aforementioned and other features and objects of the present invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of a preferred embodiment taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with an embodiment of the present invention in the order of the manufacturing steps.

FIG. 2 shows cross sectional views showing the multilayer wiring board assembly in accordance with the embodiment of the present invention in the order of the manufacturing steps.

FIG. 3 shows cross sectional views showing the multilayer wiring board assembly in accordance with the embodiment of the present invention in the order of the manufacturing steps.

FIG. 4 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with another embodiment of the present invention in the order of the manufacturing steps.

FIG. 5 shows cross sectional views showing the multilayer wiring board assembly in accordance with another embodiment of the present invention in the order of the manufacturing steps.

FIG. 6 shows cross sectional views showing the multilayer wiring board assembly in accordance with another embodiment of the present invention in the order of the manufacturing steps.

FIG. 7 shows cross sectional views of the intermediate structures of a first multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with a further embodiment of the present invention in the order of the manufacturing steps.

FIG. 8 shows cross sectional views of the intermediate structures of a second multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with the further embodiment of the present invention in the order of the manufacturing steps.

FIG. 9 shows cross sectional views of the intermediate structures of a second multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with an still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 10 shows cross sectional views showing the multilayer wiring board assembly in accordance with a still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 11 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 12 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 13 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 14 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 15 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with a still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 16 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 17 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 18 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with a still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 19 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 20 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 21 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with a still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 22 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 23 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 24 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with a still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 25 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

FIG. 26 shows cross sectional views showing the multilayer wiring board assembly in accordance with the still further embodiment of the present invention in the order of the manufacturing steps.

DETAILED DESCRIPTION OF THE INVENTION

In the followings, various preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows cross sectional views of the intermediate structures of a multilayer wiring board assembly component for use in manufacturing a multilayer wiring board assembly in accordance with an embodiment of the present invention in the order of the manufacturing steps. FIG. 2 and FIG. 3 are cross sectional views showing the multilayer wiring board assembly in accordance with the embodiment of the present invention in the order of the manufacturing steps.

The multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 1(i), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET) and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 8 embedded in a through hole 7 (refer to FIG. 1(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 8 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth with a brim formed laterally extending on the upper surface of the copper foil 2 beyond the perimeter of the opening thereof in order that the leading end thereof is projected through the opposed surface of the copper plated resin film 10 having the adhesive layer 3.

A multilayer wiring board assembly is laminated by stacking a plurality of the multilayer wiring board assembly components as illustrated in FIG. 1(i) (three units in the case of the embodiment as illustrated in FIG. 2 and FIG. 3). As illustrated in FIG. 2 and FIG. 3, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 8, it is possible to make interlayer connection via-on-via.

Also, as illustrated in FIGS. 1(h) and (i), the conductive paste filler 8 is embedded in the through hole 7 during printing in order that the printing side of the conductive paste filler 8 is slightly indented to form a recess from the surface of the copper foil 2. However, as illustrated in FIG. 1(i), the conductive paste filler 8 is printed to be projected through the rare surface opposed to the printing surface so that, when the interlayer interconnection is made by via-on-via as illustrated in FIG. 3, the recess in the printing surface of the conductive paste filler 8 is filled with the projection of the conductive paste filler 8 being projected from the rare surface of the adjacent unit. Meanwhile, the height of the projection of the conductive paste filler 8 depends on the size of the recess and is preferably 10 μm or thereabout.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 8 are connected directly to each other rather than through an intervening copper foil therebetween.

Also, as illustrated in FIG. 1(h), the conductive paste filler 8 is embedded in the opening 5 in order to make electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof since the printing surface of the conductive paste filler 8 is extended laterally beyond the surface of the copper foil 2 (while indented slightly lower than the surface of the brim 8 a) after the filing printing operation.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 1 through FIG. 3.

(1) The manufacturing Process of a Multilayer Wiring Board Assembly Component (FIG. 1):

At first, as illustrated in FIG. 1(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 1(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 1(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 1(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 1(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 1(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 1(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

Next, as illustrated in FIG. 1(h), a conductive paste is screen printed to fill the through hole 7 with the conductive paste filler 8. At this time, the conductive paste filler 8 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 8 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 8.

Next, the projection 8 b of the conductive paste filler 8 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 8 in an oven at 80° C. to partially cure the conductive paste filler 8 and removing the masking tape 6 as illustrated in FIG. 1(i). By this process, the multilayer wiring board assembly component 20 is completely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 2 and FIG. 3):

As illustrated in FIG. 2, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 8.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together the respective multilayer wiring board assembly components 20 a to 20 c as illustrated in FIG. 3(a) by thermocompression with a most outer copper foil 9 at the same time and forming a circuit on the most outer copper foil 9 as illustrated in FIG. 3(b). The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 8 a of the conductive paste filler 8 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 8 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 8, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 8 b of the conductive paste filler 8 is formed in the rare surface opposed to the printing surface, it is possible to fill up the recess of the printing surface of the conductive paste filler 8 by the projection 8 a when the interlayer interconnection is made by via-on-via and therefore it becomes easy to make the electric connection between the conductive paste fillers 8 having good electric connectivity.

Also, since the conductive paste filler 8 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 8 a of the conductive paste filler 8 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 8 without compromising the electric connectivity between the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film (the polyimide film 1) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 8.

Since it is possible to provide an FPC in the form of a high density and flexible multilayered structure in accordance with the present invention, the size of an electronic appliance can be reduced by making use of the FPC according to the multilayer wiring board assembly while an electronic appliance having a curved profile can be provided with additional functionality, for example, by implementing a printed circuit board in a watch strap with high density circuits.

Next, with reference to FIG. 4, FIG. 5 and FIG. 6, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with another embodiment of the present invention will be explained.

In the case of this embodiment, the printing surfaces 8 a of the conductive paste fillers 8 as illustrated in FIG. 1, FIG. 2 and FIG. 3 are made flat (12 c) after the printing and filling process.

Namely, the multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 4(i), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET) and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 4(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 8 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth and is laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3.

A multilayer wiring board assembly is laminated by stacking a plurality of the multilayer wiring board assembly components as illustrated in FIG. 4(i) (three units in the case of the embodiment as illustrated in FIG. 5 and FIG. 6). As illustrated in FIG. 5 and FIG. 6, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 12, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween as explained in the description of “BACKGROUND OF THE INVENTION”.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 4 through FIG. 6.

(1) The Manufacturing Process of a Multilayer Wiring Board Assembly Component (FIG. 4):

At first, as illustrated in FIG. 4(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 4(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 4(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 4(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 4(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 4(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 4(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

Next, as illustrated in FIG. 4(h), a conductive paste is screen printed to fill the through hole 7 with the conductive paste filler 12. At this time, the conductive paste filler 12 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printing as described above, another suitable printing technique is used for this purpose.

Next, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. to partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 4(i). By this process, the multilayer wiring board assembly component 20 is completely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 5 and FIG. 6):

As illustrated in FIG. 5, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together, at a time or successively, the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 as illustrated in FIG. 6(a) and forming a circuit on the most outer copper foil 9. The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 12 b of the conductive paste filler 12 is formed in the rare surface opposed to the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Also, since the conductive paste filler 12 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step of a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 7, FIG. 8, FIG. 9 and FIG. 10, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a further embodiment of the present invention will be explained.

In the case of this embodiment, a multilayer wiring board assembly is laminated by the use of first and second multilayer wiring board assembly components. The first multilayer wiring board assembly component is formed by making use of a screen printing technique in order that a through hole is filled with a conductive paste filler which is laterally extending on the upper surface of the copper foil beyond the perimeter of the opening of the through hole. On the other hand, a screen printing technique is not used for forming the second multilayer wiring board assembly component in order that a through hole is filled with a conductive paste filler of which surface is flush with the surface of the copper foil. More specifically explained, the second multilayer wiring board assembly component as described above is used as the most outer unit of the multilayer wiring board assembly while the first multilayer wiring board assembly component as described above is used as at least one of the inner layers.

Next, the first multilayer wiring board assembly component as described above will be explained with reference to FIG. 7.

The first multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 7(j), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 7(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 12 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth and laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

The multilayer wiring board assembly is laminated by stacking, as inner layers, a plurality of the first multilayer wiring board assembly components as illustrated in FIG. 7(j) (if the respective layers are called as first, second and third layers from the upper outer layer in the case of the embodiment as illustrated in FIG. 10 and FIG. 11, the second and third layers are prepared in the form of the first multilayer wiring board assembly component). As illustrated in FIG. 10 and FIG. 11, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste fillers 12 and 14, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween.

Next, the manufacturing process of the first multilayer wiring board assembly component as described above will be explained with reference to FIG. 7.

At first, as illustrated in FIG. 7(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 7(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 7(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 7(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 7(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 7(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 7(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light the opening 5 by means of a CO₂ laser and the like.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 μm φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 7(h) and (i), the conductive paste 12 is placed on the copper foil 2 and a mask 30 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 12 at the leading end of the through hole 7 near the adhesive layer 3.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 12. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 12 in contact with the separate paper 31 and preventing the conductive paste filler 12 from being detached from the through hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Next, after removing the separate paper 31, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. for an hour to partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 7(j). By this process, the first multilayer wiring board assembly component 20 is completely formed.

Next, the second multilayer wiring board assembly component as described above will be explained with reference to FIG. 8.

The second multilayer wiring board assembly component 20′ is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 8(j), the multilayer wiring board assembly component 20′ is composed of a copper plated resin film 10 composed of a flexible resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET) and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 14 embedded in a through hole 7 (refer to FIG. 8(g)) passed through the resin film 10 to form an inner via hole. The conductive paste filler 14 is embedded in the through hole 7 from the surface of the copper foil 2 a by printing with the printing surface 14 c of the conductive paste filler 14 being flat and flush with the upper surface 2 c of the copper foil 2 a in order that the leading end thereof is projected as a projection 14 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3. Namely, as illustrated in FIG. 8(j), the upper surface 2 c of the copper foil 2 a and the printing surface 14 c of the conductive paste filler 14 are connected to form a continuous flat surface having the same height.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

The multilayer wiring board assembly is laminated by stacking, as an outer layer, the second multilayer wiring board assembly component as illustrated in FIG. 8(j) (if the respective layers are called as first, second and third layers from the upper outer layer in the case of the embodiment as illustrated in FIG. 10 and FIG. 11, the second multilayer wiring board assembly component is the first layer). As illustrated in FIG. 10 and FIG. 11, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste fillers 12 and 14, it is possible to make interlayer connection via-on-via.

Next, the manufacturing process of the second multilayer wiring board assembly component as described above will be explained with reference to FIG. 8.

At first, as illustrated in FIG. 8(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 8(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 8(c), the dry film 4 is exposed to radiation of a pattern of the opening of the through hole 7, followed by developing the dry film 4. In the case, the dry film 4 a is developed in order to be continuous except for the opening 5.

Next, as illustrated in FIG. 8(d), the copper foil 2 is etched with the dry film 4 a as a mask to form the copper foil 2 a having the predetermined opening 5.

Next, after the dry film 4 a is removed from the copper foil 2 a as illustrated in FIG. 8(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 8(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 8(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like.

Since the through hole 7 is opened after forming the opening 5, it is possible to form a small hole as described above.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 8(h) and (i), the conductive paste 14 is placed on the copper foil 2 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 14 at the leading end of the through hole 7 near the adhesive layer 3.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 14. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 14 in contact with the separate paper 31 and preventing the conductive paste filler 14 from being detached from the through hole 7 when the separate paper 31 is removed.

In this case, as illustrated in FIG. 8(j), the upper surface 2 c of the copper foil 2 a and the printing surface 14 c of the conductive paste filler 14 are connected to form a continuous flat surface having the same height.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 14.

Next, after removing the separate paper 31, the projection 14 b of the conductive paste filler 14 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 14 in an oven at 80° C. for an hour to partially cure the conductive paste filler 14 and removing the masking tape 6 as illustrated in FIG. 8(j). By this process, the second multilayer wiring board assembly component 20′ is completely formed.

FIG. 9 shows a modification of the manufacturing process of the multilayer wiring board assembly component 20′ as described above.

In this modification, while the opening 5 is not formed in the copper foil 2, the through hole 7 is opened also in the copper foil 2. By this configuration, the step of forming the opening 5 is dispensed with so that it is possible to decrease the number of the manufacturing steps.

Namely, as illustrated in FIG. 9(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 having made of a polyimide film a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 9(b), the through hole 7 of 0.2 mm φ is opened in the copper foil 2 and the masking tape 6 through the resin film 1, the adhesive layer 3 and the adhesive layer 3.

Next, as illustrated in FIGS. 9(c) and (d), the conductive paste 14 is placed on the copper foil 2 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 14 at the leading end of the through hole 7 near the adhesive layer 3.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 14. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 14 in contact with the separate paper 31 and preventing the conductive paste filler 14 from being detached from the through hole 7 when the separate paper 31 is removed.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 14.

Next, after removing the separate paper 31, the projection 14 b of the conductive paste filler 14 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 14 in an oven at 80° C. for an hour to partially cure the conductive paste filler 14 and removing the masking tape 6 as illustrated in FIG. 9(e). By this process, the second multilayer wiring board assembly component 20′ is completely formed.

Next, the press step for manufacturing a multilayer wiring board assembly by joining the first and second multilayer wiring board assembly components 20 and 20′ together will be explained with reference to FIG. 10 and FIG. 11.

As illustrated in FIG. 10, the multilayer wiring board assembly is composed of the second multilayer wiring board assembly component 20′ as illustrated in FIG. 8(j) or FIG. 9(e) arranged as a most outer layer (most upper layer) and the first multilayer wiring board assembly component 20 as illustrated in FIG. 7(j) arranged as the other layers (inner layers) which are laminated with the second multilayer wiring board assembly component 20′. The respective layers are formed with a plurality of circuit patterns and through holes 7 which are filled with the conductive paste fillers 12 and 14.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together, at a time or successively, the respective first and second multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 as illustrated in FIG. 11(a) and forming a circuit on the most outer copper foil 9.

In this case, as illustrated in FIG. 10(a), the upper surface of the most outer layer (most upper layer) is formed in order that the upper surface 2 c of the copper foil 22 a and the leading end of the conductive paste filler 14, i.e., the printing surface 14 c, are arranged to form a continuous flat surface having the same height so that it is possible to apply a uniform pressure to the entirety of the multilayer wiring board assembly during thermocompression. By this configuration, the multilayer wiring board assembly is fixedly laminated with a better electric connectivity.

The step of laminating the respective multilayer wiring board assembly components 20 and 20′ and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 and 14 of the respective multilayer wiring board assembly components 20 and 20′ are fixedly pressed and finally cured by thermocompression at the same time.

Finally, as illustrated in FIG. 11(b), a circuit pattern is formed in the most outer copper foil 2 a by etching and the like followed by plating the copper foil 2 a with a metallic layer 15 for the purpose of increasing the area available for electric contact with the conductive paste filler 14. While the metallic layer 15 may be formed of any conductive material such as Au, Ni, Hg, Ag, Rh and Pd, the use of Au is particularly preferable in consideration of oxidation-proof and facilitating bonding.

In accordance with this embodiment as described above, since the through holes 7 of the first and second multilayer wiring board assembly component 20 and 20′ are filled with the conductive paste fillers 12 and 14, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projections 12 b and 14 b of the conductive paste fillers 12 and 14 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 and 14 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Also, since the conductive paste filler 12 of the first multilayer wiring board assembly component 20 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step for a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 12, FIG. 13 and FIG. 14, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a further embodiment of the present invention will be explained.

In the case of this embodiment, a multilayer wiring board assembly is laminated by the use of a plurality of multilayer wiring board assembly components, each of which is prepared by embedding a conductive paste in a through hole by screen printing with a mask in order that the conductive paste filler is laterally extending beyond the perimeter of the opening of the through hole.

Next, the above described multilayer wiring board assembly component will be explained with reference to FIG. 12.

The multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 12(j), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 12(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 12 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth with a mask and is laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

A multilayer wiring board assembly is laminated by stacking a plurality of the multilayer wiring board assembly components as illustrated in FIG. 12(i) (three units in the case of the embodiment as illustrated in FIG. 13 and FIG. 14). As illustrated in FIG. 13 and FIG. 14, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 12, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 12.

At first, as illustrated in FIG. 12(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 12(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 12(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 12(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 12(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 12(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 12(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 μm φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, a conductive paste is screen printed to fill the through hole 7 with the conductive paste filler 12. In this case, as illustrated in FIG. 12(h), an amount of the conductive paste 12 is placed on the copper foil 2 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A, after a metallic mask (or a screen mask) 30 having a hole of a diameter larger than that of the through hole 7 is placed on the copper foil 2 in order that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5, and after a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 12 at the leading end of the through hole 7 near the masking tape 6.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 12. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 12 in contact with the separate paper 31 and preventing the conductive paste filler 12 from being detached from the through hole 7 when the separate paper 31 is removed.

By this configuration, as illustrated in FIG. 12(i), after removing the metallic mask 30 and the separate paper 31, the conductive paste filler 12 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printing as described above, another suitable printing technique is used for this purpose.

Next, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. to partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 12(j). By this process, the multilayer wiring board assembly component 20 is completely formed.

Next, the press step for manufacturing a multilayer wiring board assembly by joining a plurality of the multilayer wiring board assembly components 20 as described above will be explained with reference to FIG. 13 and FIG. 14.

As illustrated in FIG. 13, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 at the same time or sequentially as illustrated in FIG. 14(a) and forming a circuit on the most outer copper foil 9 as illustrated in FIG. 14(b). The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 12 b of the conductive paste filler 12 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Also, since the conductive paste filler 12 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film 1 (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step of a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 15, FIG. 16 and FIG. 17, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a still further embodiment of the present invention will be explained.

In the case of this embodiment, a multilayer wiring board assembly is laminated by the use of a plurality of multilayer wiring board assembly components, each of which is prepared by embedding a conductive paste in a through hole by the use of a plane table having a hole of a diameter larger than that of the through hole in order that the conductive paste filler is laterally extending beyond the perimeter of the opening of the through hole.

Next, the above described multilayer wiring board assembly component will be explained with reference to FIG. 15.

The multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 15(k), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 15(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 12 is embedded in the through hole 7 from the masking tape 6 with the plane table 34 as explained in the following description by screen printing and so forth and laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

The multilayer wiring board assembly is laminated by stacking a plurality of the first multilayer wiring board assembly components as illustrated in FIG. 15(k) (three units in the case of the embodiment as illustrated in FIG. 16 and FIG. 17). As illustrated in FIG. 16 and FIG. 17, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 12, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 15.

At first, as illustrated in FIG. 15(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 15(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 15(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 15(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 15(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3 as illustrated in FIG. 15(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 15(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 82 m φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, a conductive paste is screen printed to fill the through hole 7 with the conductive paste filler 12. In this case, as illustrated in FIG. 15(h), an amount of the conductive paste 12 is spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A, after preparing the plane table 34 having a hole 33 of a diameter larger than that of the through hole 7, placing the copper plated resin film 10 as illustrated in FIG. 15(g) on the hole 33 of the plane table 34 with the copper foil 2 being positioned as the bottom of the multilayer wiring board assembly component (i.e. it is inverted), and preselecting the coefficient of viscosity of the conductive paste filler 12 and the printing condition in order that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 of the copper foil 2.

In this case, the coefficient of viscosity of the conductive paste 12 is predetermined lower than that of the conductive paste 12 in the case of the embodiment as illustrated in FIG. 12. The profile of the conductive paste filler 12 as described above is illustrated in FIG. 15(i). In this case, as illustrated in FIG. 15(i), the size of the hole 33 of the above described plane table 34 is predetermined to provide a sufficient space in order that the conductive paste filler 12 is not so extending from the opening 5 of the copper foil 2 as to make contact with the plane table 34 after the filling step.

Next, when the lanimate is removed from the plane table 34 and inverted, the conductive paste is screen printed in order that the diameter of the conductive paste filler 12 is larger than the diameter of the opening 5 (the through hole 7) by about 10% to 50% so that the conductive paste is laterally extending beyond the perimeter of the opening 5 thereof as illustrated in FIG. 15(i). By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat. It is therefore possible to form the brim 12 a of a smaller thickness with a higher degree of accuracy, as compared to the case utilizing a mask (refer to FIG. 12), by filling the through hole 7 with the conductive paste filler 12 by the use of the plane table 34.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printing as described above, another suitable printing technique is used for this purpose.

Next, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3 in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. to partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 15(k). By this process, the multilayer wiring board assembly component 20 is completely formed.

Next, the press step for manufacturing a multilayer wiring board assembly by joining a plurality of the multilayer wiring board assembly components 20 as described above will be explained with reference to FIG. 16 and FIG. 17.

As illustrated in FIG. 16, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 at the same time or sequentially as illustrated in FIG. 17(a) and forming a circuit on the most outer copper foil 9 as illustrated in FIG. 17(b). The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 12 b of the conductive paste filler 12 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Also, since the conductive paste filler 12 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film 1 (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step of a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Furthermore, in accordance with the present invention, the opening of the through hole near the copper foil is placed on the plane table having a hole of a diameter larger than that of the through hole followed by filling the through hole with the conductive paste from the leading end of the masking tape in order to form a brim laterally extending beyond the perimeter of the opening of the copper foil, and therefore it is possible to form the brim having a desired profile with a high degree of accuracy and having a smaller thickness than that in the case utilzing a mask. By this configuration, the multilayer wiring board assembly is fixedly laminated with a better electric connectivity.

Next, with reference to FIG. 18, FIG. 19 and FIG. 20, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a still further embodiment of the present invention will be explained.

In the case of this embodiment, the multilayer wiring board assembly is laminated by laminating together a plurality of multilayer wiring board assembly components, each of which is made by preparing a copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface, attaching masking tapes to the both surfaces of the copper plated resin film, opening a through hole in the copper plated resin film through the masking tape, filling the through hole with a conductive paste to form a conductive paste filler having end surfaces flush with the surfaces of the masking tape, removing the masking tape after the formation of the conductive paste filler to form projections of the conductive paste filler in the both surfaces thereof.

Next, the above described multilayer wiring board assembly component will be explained with reference to FIG. 18. The multilayer wiring board assembly component 20′ is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 18(j), the multilayer wiring board assembly component 20′ is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3 made of a thermoplastic polyimide film and the like bonded to the other surface, and a conductive paste filler 14 embedded in a through hole 7 (refer to FIG. 18(g)) passed through the resin film 10 to form an inner via hole. The conductive paste filler 14 is formed to have an leading end projecting from the upper surface 2 c of the copper foil 2 as a projection 14 c and a tail end projecting from the lower surface of the adhesive layer 3 as the projection 14 b. Namely, as illustrated in FIG. 18(h) through (j), the projections 14 c and 14 b are formed by removing the masking tapes 6 a and 6 b as described above after embedding the conductive paste filler 14 from the copper foil 2 by printing and the like in the through hole 7 of the copper plated resin film 10 with the masking tapes 6 a and 6 b on the both surfaces thereof.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

Next, the manufacturing process of the multilayer wiring board assembly component as described above will be explained with reference to FIG. 18.

At first, as illustrated in FIG. 18(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3 made of a thermoplastic polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 18(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 18(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 18(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 18(e).

Next, as illustrated in FIG. 18(f), the first masking tape 6 a is bonded to the surface of the copper foil 2, which is attached to the adhesive layer 3 in the form of a circuit pattern, while the second masking tape 6 b is bonded to the surface of the adhesive layer 3. The first and second masking tapes 6 may be made of a PET and the like.

Next, as illustrated in FIG. 18(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the first and second masking tape 6 a and 6 b by exposing them to a laser light by means of a CO₂ laser and the like corresponding to the opening 5. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 μm φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 14 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 18(h) and (i), the conductive paste 14 is placed on the first masking tape 6 a and spread to fill the through hole 7 therewith by moving a squeezee 15 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 14 at the leading end of the through hole 7 near the adhesive layer 3.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 14. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 14 in contact with the separate paper 31 and preventing the conductive paste filler 14 from being detached from the through hole 7 when the separate paper 31 is removed.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 14.

Next, the first projection 14 c of the conductive paste filler 14 which is projecting through the upper surface 2 c of the copper foil 2 and having a diameter equal to or smaller than the diameter of the through hole 7 is formed, as well as the second projection 14 b of the conductive paste filler 14 which is projecting through the rare surface opposed to the printing surface and having a diameter equal to or smaller than the diameter of the through hole 7, as illustrated in FIG. 18(j), by removing the separate paper 31 and heating the conductive paste filler 14 in an oven at 80° C. to partially cure the conductive paste filler 14 and removing the first and second masking tapes 6 a and 6 b. By this process, the multilayer wiring board assembly component 20′ is completely formed.

Generally speaking, in the case where a brim (land) is formed on a copper foil by the use of a metallic mask, the hole of the metallic mask has to be aligned with a hole of the board so that the brim (land) of the conductive paste filler has to be formed with a diameter larger than as required.

Contrary to this, in accordance with the embodiments of the present invention as described above, the multilayer wiring board assembly component is formed by bonding the masking tape 6 a on the copper foil 2, opening a through hole through the masking tape 6 a and the copper foil 2, removing the masking tape 6 a to form the first projection 14 c. A plurality of such multilayer wiring board assembly components are laminated together in order that the first projection 14 c is crushed and spread on the copper foil 2 to form the brim (land) without need for exact accurate alignment while it becomes possible to adjust the diameter of the brim (land) by changing the thickness of the masking tape 6 a.

Next, the press step for manufacturing a multilayer wiring board assembly by joining a plurality of the multilayer wiring board assembly components 20 as described above will be explained with reference to FIG. 19 and FIG. 20.

As illustrated in FIG. 19, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 14.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 at the same time or sequentially as illustrated in FIG. 20(a) and forming a circuit on the most outer copper foil 9 as illustrated in FIG. 20(b). The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and brims 14 a of the conductive paste filler 14 in the adhesive layer 3 made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 14 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 14 c of the conductive paste filler 14 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 14 having good electric connectivity when the interlayer interconnection is made by via-on-via.

In this case, as illustrated in FIG. 20(a), the first projection 14 c of the above described multilayer wiring board assembly component 20′ is squashed by compression of the conductive paste filler 14 as described above to form the brim 14 a having a diameter larger than that of the through hole 7 and laterally extending on the copper foil 2 beyond the perimeter of the through hole 7 in order to increase the contact area of the conductive paste filler 14 with the copper foil 2 resulting in improved electric connectivity.

The step of laminating the respective multilayer wiring board assembly components and the outer copper foil 9 to each other by thermocompression is carried out by heating them at 280° C. or thereabout and pressing them at 9 MPa or thereabout.

In accordance with this embodiment as described above, since the first projection 14 c of the above described multilayer wiring board assembly component 20′ is squashed by compression of the conductive paste filler 14 to form the brim 14 a having a diameter larger than that of the through hole 7 and laterally extending on the copper foil 2 beyond the perimeter of the through hole 7 resulting in improvement of electric connectivity.

Furthermore, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film 1 (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3 to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Also, in accordance with the present invention, since the leading end of the conductive paste filler is projected from the adhesive layer while the tail end of said conductive paste filler is projected from said copper foil, the multilayer wiring board assembly is fixedly laminated with a better electric connectivity.

Next, with reference to FIG. 21, FIG. 22 and FIG. 23, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a still further embodiment of the present invention will be explained.

In the case of this embodiment, the adhesive layer 3 of the embodiment as illustrated in FIG. 18, FIG. 19 and FIG. 20 is made of a thermosetting resin (3A).

In the case utilizing a thermoplastic polyimide as the interlayer adhesive layer 3, the multilayer lamination (finally curing) is carried out at a temperature not lower than the glass transition temperature. However, since there occurs degradation of conductive resin components (the conductive paste) and oxdization of metallic fillers because of the heating process for multilayer lamination, the thermoplastic polyimide has to be made of a material selected among from those having lower glass transition temperatures.

However, the modulus of elasticity of a thermoplastic polyimide is lowered by heating and recovered again by cooling. Namely, a thermoplastic polyimide has a characteristic that the modulus of elasticity is reversible relative to the temperature change. Accordingly, in the case where a thermoplastic polyimide having a low glass transition temperature is used as an adhesive layer, there sometime occurs peeling-off during a soldering process after manufacturing the multilayer wiring board assembly, during a heat resistant test and so forth. It is therefore inevitable to use a material having a higher glass transition temperature.

Accordingly, in order to solve the above described dilemma encountered when a thermoplastic polyimide is used, it is required that the polyimide adhesive layer 3 can be compression bonded at a low temperature while maintaining the heat resistant feature of the polyimide.

For this purpose, the interlayer adhesive layer 3A is formed by the use of a heat resistant resin such as a thermosetting resin (which is not hardened (uncured) in an initial state, and hardened (cured) at a temperature higher than the cure temperature while the initial state can not be recovered, even if cooled, as maintaining the hardened state) rather than the use of a thermoplastic adhesive material. It is therefore possible to manufacture a multilayer wiring board assembly having a good heat resisting property with little damage to the respective boards during the manufacturing process by selecting the cure temperature of the thermosetting resin to be lower than the temperature at which the resin contained in the conductive paste is not damaged and the filler is not oxidized.

Namely, the multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 21(j), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3A made of a thermosetting polyimide film and the like bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 21(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 12 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth and laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3A.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Also, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

The above described adhesive layer 3A may be formed of a glass epoxy prepreg an aramid-epoxy prepreg.

Also, the above described adhesive layer 3A is preferably made of a resin which is cured at 60° C. to 250° C.

Namely, the adhesive layer 3A is preferably made of a resin whose the cure temperature is no higher than the heat resisting temperature of a resin contained in the conductive paste and no lower than the evaporation temperature of the volatile component that is mixed into the conductive paste.

A multilayer wiring board assembly is laminated by stacking a plurality of the multilayer wiring board assembly components as illustrated in FIG. 21(j) (three units in the case of the embodiment as illustrated in FIG. 22 and FIG. 23). As illustrated in FIG. 22 and FIG. 23, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 12, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween as explained in the description of “BACKGROUND OF THE INVENTION”.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 21 through FIG. 23.

(1) The Manufacturing Process of a Multilayer Wiring Board Assembly Component (FIG. 21):

At first, as illustrated in FIG. 21(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3A made of a thermosetting polyimide film bonded to the other surface and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Next, as illustrated in FIG. 21(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 21(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 21(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 21(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3A as illustrated in FIG. 21(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 21(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3A and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 μm φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 21(h) and (i), the conductive paste 12 is placed on the copper foil 2 and a mask 30 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 12 at the leading end of the through hole 7 near the adhesive layer 3A.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 12. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 12 in contact with the separate paper 31 and preventing the conductive paste filler 12 from being detached from the through hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printing as described above, another suitable printing technique is used for this purpose.

Next, after removing the separate paper 31, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3A in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 21(j). In this case where the adhesive layer 3A is partially cured at the partial curing temperature of 80° C., it is made of a resin which can be finally (irreversibly) cured at a temperature higher than the partial curing temperature of 80° C. Meanwhile, it is possible to dispense with the partial curing process (for dissipating the solvent and air) when the conductive paste filler 12 is made of some type of a conductive paste.

By this process, the multilayer wiring board assembly component 20 is completely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 22 and FIG. 23):

As illustrated in FIG. 22, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together, at a time or successively, the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 as illustrated in FIG. 23(a) and forming a circuit on the most outer copper foil 9. The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 170° C. or thereabout and pressing them at 9 MPa or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3A made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since the interlayer adhesive layer 3A is formed by the use of a heat resistant resin such as a thermosetting resin (which is not hardened (uncured) in an initial state, and hardened (cured) at a temperature higher than the cure temperature while the initial state can not be recovered, even if cooled, as maintaining the hardened state) rather than the use of a thermoplastic adhesive material, it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property with little damage to the respective boards during the manufacturing process by selecting the cure temperature of the thermosetting resin to be lower than the temperature at which the resin contained in the conductive paste is not damaged and the filler is not oxidized. Also, since the volatile component of the conductive paste filler is evaporated in genral at 100° C. or thereabout, the adhesive layer 3A is made of a resin which is cured at a temperature not lower than the evaporation temperature.

Furthermore, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Also, since the projection 12 b of the conductive paste filler 12 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Still further, since the conductive paste filler 12 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Still further, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3A to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step of a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 24, FIG. 25 and FIG. 26, a multilayer wiring board assembly component and the multilayer wiring board assembly in accordance with a still further embodiment of the present invention will be explained.

In the case of this embodiment, the adhesive layer 3 of the embodiment as illustrated in FIG. 18, FIG. 19 and FIG. 20 is made of a thermoplastic polyimide to which is given a thermosetting property (3B).

When a thermoplastic polyimide is used as the interlayer adhesive layer 3, the multilayer lamination (finally curing) is carried out at a temperature not lower than the glass transition temperature. However, since there occurs degradation of conductive resin components (the conductive paste) and oxdization of metallic fillers because of the heating process for multilayer lamination, the thermoplastic polyimide has to be made of a material selected among from those having lower glass transition temperatures.

However, the modulus of elasticity of a thermoplastic polyimide is lowered by heating and recovered by cooling again. Namely, a thermoplastic polyimide has a characteristic that the modulus of elasticity is reversible relative to the temperature change. Accordingly, in the case where a thermoplastic polyimide having a low glass transition temperature is used as an adhesive layer, there sometime occurs peeling-off in a soldering process after manufacturing the multilayer wiring board assembly, in a heat resistant test and so forth. It is therefore inevitable to use a material having a higher glass transition temperature.

Accordingly, in order to solve the above described dilemma in the use of a thermoplastic polyimide, it is required that the polyimide adhesive layer 3 can be compression bonded at a low temperature while maintaining the heat resistant feature of the polyimide.

For this purpose, the interlayer adhesive layer 3 is formed of a thermoplastic polyimide 3B to which is given a thermosetting property, and therefore it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property without damaging the conductive resin components (the conductive paste).

Namely, the multilayer wiring board assembly component 20 is a connection unit for use in the process of laminating a multilayer wiring board assembly and comprises an FPC as a base element made of a single sided copper plated resin film. Namely, as illustrated in FIG. 24(j), the multilayer wiring board assembly component 20 is composed of a copper plated resin film 10 composed of a flexible (bendable) resin film 1 made of a polyimide (PI), polyethylene terephthalate (PET), a liquid crystal polymer and the like and provided with a copper foil 2 bonded to one surface thereof and an adhesive layer 3B made of a thermoplastic polyimide to which is given a thermosetting property bonded to the other surface, and a conductive paste filler 12 embedded in a through hole 7 (refer to FIG. 24(g)) passed through the resin film 10 to form an inner via hole. A predetermined circuit pattern is formed in the copper foil 2 by etching and the like. The conductive paste filler 12 is embedded in the through hole 7 from the surface of the copper foil 2 by screen printing and so forth and laterally extending on the upper surface of the copper foil 2 as a brim 12 a beyond the perimeter of the opening thereof with the printing surface 12 c of the conductive paste filler 12 being flat and flush therewith in order that the leading end thereof is projected as a projection 12 b through the opposed surface of the copper plated resin film 10 having the adhesive layer 3B.

While the resin film 10 is made of a material which is flexible, i.e., bendable in the case of the above described embodiment, the resin film 10 can be made of a rigid material such as a glass epoxy, an aramid-epoxy.

Meanwhile, a BT resin, a PPO, a PPE and the like can be used as the material for forming the above described resin film 10.

Also, the adhesive layer 3B is made of a thermoplastic polyimide to which is given a thermosetting property having a cure temperature of 150° C. to 200° C., a modulus of elasticity of 600 to 1400 MPa and a glass transition temperature of 70° C. to 90° C.

A multilayer wiring board assembly is laminated by stacking a plurality of the multilayer wiring board assembly components as illustrated in FIG. 24(j) (three units in the case of the embodiment as illustrated in FIG. 25 and FIG. 26). As illustrated in FIG. 25 and FIG. 26, since the through hole 7 of the multilayer wiring board assembly component is filled with the conductive paste filler 12, it is possible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made by via-on-via, the conductive paste fillers 12 are connected directly to each other rather than through an intervening copper foil therebetween as explained in the description of “BACKGROUND OF THE INVENTION”.

Next, the manufacturing process (method) of the multilayer wiring board assembly in accordance with the present invention will be explained with reference to FIG. 24 through FIG. 26.

(1) The Manufacturing Process of a Multilayer Wiring Board Assembly Component (FIG. 24):

At first, as illustrated in FIG. 24(a), a single sided copper plated resin film 10 is provided or prepared as the resin film 1 made of a polyimide film having a thickness of 12.5 to 50 μm with the copper foil 2 having a thickness of 5 to 18 μm bonded to one surface and with the adhesive layer 3A made of a thermoplastic polyimide to which is given a thermosetting property and having a thickness of 15 to 30 μm (corresponding to the thickness required for accommodating the circuit pattern of the copper foil 2 when the interlayer interconnection is made).

Namely, in this case, a polyimide base bonding sheet made of a thermoplastic polyimide to which is given a thermosetting property is temporarily compression bonded, as the adhesive layer 3B, to the other surface of the single sided polyimide resin film 1 under a pressure of 40 kgf/cm² for a short time (about 10 minutes) at a temperature higher than the glass transition temperature (70 to 90° C. ) and lower than the cure temperature (when finally cured) during the press process (the lamination process) of the multilayer wiring board assembly as explained in the following description.

The polyimide base bonding sheet functioning as a thermoplastic polyimide to which a thermosetting property is given is, for example, a polyimide base adhesive sheet of the SPB series as manufactured and distributed by Nippon Steel Chemical Co., LTD.

Meanwhile, the manufacture method and other information of the thermoplastic polyimide to which is given a thermosetting property made of a polyimide base adhesive sheet of the SPB series as manufactured by Nippon Steel Chemical Co., LTD. is described in Japanese Patent Application Hei10-37700 (Japanese Patent Published Application Hei11-228825) filed in Feb. 19, 1998, Japanese Patent Application Hei10-145872 (Japanese Patent Published Application Hei11-335555) filed in May 27, 1998 and the like.

Next, as illustrated in FIG. 24(b), a dry film (resist) 4 is laminated to the copper foil 2 bonded to the resin film 1 with a vacuum laminator or a roll laminator. Next, as illustrated in FIG. 24(c), the dry film 4 is exposed to radiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 24(d), a predetermined circuit pattern is formed by etching the copper foil 2 with the dry film 4 as a mask. In this step, the opening 5 is formed by the same etching process for use in the subsequent step of opening the through hole 7. Next, after the dry film 4 is removed from the copper foil 2 as illustrated in FIG. 24(e), a masking tape 6 having a thickness of 10 to 50 μm is bonded as a mask to the surface of the adhesive layer 3B as illustrated in FIG. 24(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 24(g), the through hole 7 of 0.05 to 0.3 mm φ is opened in the resin film 1 through the resin film 1, the adhesive layer 3 and the masking tape 6 by exposing them to a laser light through the opening 5 by means of a CO₂ laser and the like. Meanwhile, the through hole 7 may be opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5 by means of a CO₂ laser, it is possible to open a smaller hole (50 to 250 μm φ). Namely, if the through hole 7 were formed through the copper foil 2 in which the opening 5 had not be formed in advance, a CO₂ laser (capable of opening holes of 50 to 250 μm φ) is not used for this purpose and therefore a larger hole of 200 μm φ or larger has to be opened by means of a drill (capable of opening holes of 200 μm φ or larger). Meanwhile, some other lasers such as a UV-YAG laser, an excimer laser may be used for this purpose of opening small holes. However, these lasers is too expensive to use for this purpose and therefore not practical.

Meanwhile, since the through hole 7 as described above is passed also through the copper foil 2, there are not generated voids, desmear, as well as the like drawbacks, which are likely if the conductive paste filler 12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIG. 24(h) and (i), the conductive paste 12 is placed on the copper foil 2 and a mask 30 and spread to fill the through hole 7 therewith by moving a squeezee 32 made of an urethane, silicone and the like in the direction of arrow A. At this time, a breathable separate paper 31 as siliconized or fluoridized is placed for the purpose of preserving the conductive paste 12 at the leading end of the through hole 7 near the adhesive layer 3B.

In this case, the separate paper 31 is provided with breathability for the purpose of enabling air to escape when the through hole 7 is filled with the conductive paste 12. Also, at least the upper surface of the separate paper 31 is siliconized or fluoridized as described above for the purpose of making easy to remove the separate paper 31 from the conductive paste filler 12 in contact with the separate paper 31 and preventing the conductive paste filler 12 from being detached from the through hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with a diameter larger than the opening 5 (the through hole 7) by about 10% to 50% so that part of the conductive paste remains on the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof. By this configuration, there is formed the brim 12 a which is connected to the land surface 2 a of the copper foil 2 in the direction normal to the surface. In this case, however, the printing surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes can be used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printing as described above, another suitable printing technique is used for this purpose.

Next, after removing the separate paper 31, the projection 12 b of the conductive paste filler 12 which is projecting through the adhesive layer 3B in the surface opposed to the printing surface is formed by heating the conductive paste filler 12 in an oven at 80° C. partially cure the conductive paste filler 12 and removing the masking tape 6 as illustrated in FIG. 24(j). By this process, the multilayer wiring board assembly component 20 is completely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 25 and FIG. 26):

As illustrated in FIG. 25, a plurality of circuit patterns and a plurality of through holes 7 are formed on each of the multilayer wiring board assembly components (three multilayer wiring board assembly components) 20 a, 20 b and 20 c. Also, the through holes 7 are filled with the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance with the present embodiment is completed by laminating together, at a time or successively, the respective multilayer wiring board assembly components 20 a to 20 c by thermocompression with a most outer copper foil 9 as illustrated in FIG. 26(a) and forming a circuit on the most outer copper foil 9. The step of laminating the respective multilayer wiring board assembly components 20 a to 20 c and the most outer copper foil 9 to each other by thermocompression is carried out by heating them at 180° C. or thereabout and pressing (finally compression bonding) them at 40 kgf/cm² for 60 minutes or thereabout in order to embed the circuit pattern of the copper foil 2 and the brim 12 a of the conductive paste filler 12 in the adhesive layer 3B made of a thermoplastic polyimide having adhesivity and fluidity. At this time, the conductive paste fillers 12 of the respective multilayer wiring board assembly components 20 a to 20 c are fixedly pressed and finally cured by thermocompression at the same time.

During the final compression bonding process, the conductive resin components (the conductive paste 12) shall not be deteriorated since the heating temperature is as low as 180° C.

Also, in this case, the multilayer wiring board assembly is not curled (warped). Namely, while the adhesive layer is contracted or expanded during heating, the contraction or expansion can be cancelled out if there is a center line of symmetry in the cross section thereof. However, a polyimide film is a highly flexuous material and therefore tends to be curled (warped) when heated. However, since the heating temperature can be set as low as about 280 to 180° C. in accordance with this embodiment, no curl (warp) appears.

As detailedly explained in the above, in accordance with this embodiment, the adhesive layer 3B is made of a thermoplastic polyimide base bonding sheet to which is given a thermosetting property so that it is possible to manufacture a multilayer wiring board assembly without deteriorating the conductive resin components (the conductive paste) and without forming curl (warp).

Also, since the through holes 7 of the multilayer wiring board assembly component 20 a to 20 c are filled with the conductive paste fillers 12, it is possible to make the interlayer interconnection between each adjacent layers by via-on-via. Furthermore, since the projection 12 b of the conductive paste filler 12 is formed in the printing surface, it becomes easy to make the electric connection between the conductive paste fillers 12 having good electric connectivity when the interlayer interconnection is made by via-on-via.

Furthermore, since the conductive paste filler 12 is embedded in the through hole 7 during printing operation in order that the printing surface thereof is laterally extended from the opening 5 of the copper foil 2, the brim 12 a of the conductive paste filler 12 makes reliable electric contact with the inner side surface and the upper surface of the copper foil 2 beyond the perimeter of the opening 5 thereof, and therefore it is possible to connect the copper foil 2 to the conductive paste filler 12 without compromising the electric connectivity between the copper foil 2 and the fillers of the conductive paste.

Still further, since the copper plated resin film 10 is used in the manufacturing process of the multilayer wiring board assembly component, it becomes easy to preserve the accuracy of alignment of dimensions and positions when holding a sample, opening a hole and filling the hole and, as a result, it is possible to save labor in the manufacturing works. Namely, in the case of a conventional case, the respective steps of holding a sample, opening a hole and filling the hole have to be conducted with a resin film (the polyimide film) having a small thickness as it is. However, in accordance with this embodiment, the respective steps of holding a sample, opening a hole and filling the hole are conducted after bonding the copper foil 2 and the adhesive layer 3B to the resin film 1 and therefore it becomes easy to open and fill holes with the conductive paste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can be formed only by preparing multilayer wiring board assembly components as described above and combining and joining them together, the press step of a multilayer wiring board assembly becomes easy without need for conducting press steps of multilayer wiring board assembly components.

Meanwhile, the profiles of the through hole 7 and the conductive paste fillers 8 and 12 of the multilayer wiring board assembly component 20 as illustrated in FIGS. 1(i), 4(i), 7(j), 8(j), 9(e), 12(j), 15(k), 18(j), 21(j) and 24(j) are usually circles as horizontally viewed (i.e., as viewed from above in FIGS. 1(i), 4(i), 7(j), 8(j), 9(e), 12(j), 15(k), 18(j), 21(j) and 24(j)). While the present invention is not limited to those embodiments, other profiles are possible.

As detailedly explained in the above, in accordance with the present invention, a through hole is opened through the copper plated resin film made of a flexible resin film which is provided with a copper foil bonded to one surface thereof and an adhesive layer bonded to the other surface, and filled with a conductive paste, and therefore it becomes easy to form the through hole and embed the conductive paste because of the increase in thickness as compared with the case where a through hole is opened only through a resin film and filled with a conductive paste.

Also, in accordance with the present invention, the conductive paste filler of the multilayer wiring board assembly component is embedded in the through hole of the copper plated resin film by screen printing with a leading end of the conductive paste filler being projected from the adhesive layer, and therefore it is possible to make reliable electric connection of the leading end of the conductive paste filler with the copper foil or the conductive paste filler of the multilayer wiring board assembly component and to improve electric connectivity between the respective layers when a plurality of the multilayer wiring board assembly components are laminated together. Particularly, in this case, direct connection between the conductive paste fillers without the intermediary copper foil is effective to improve the electric connectivity.

As explained heretofore, in accordance with the present invention, it is possible to easily laminate together flexible FPCs having highly packing densities by via-on-via and chip-on-via.

Also, in accordance with the present invention, the upper surface of the most outer layer (most upper layer) is formed in order that the upper surface of the copper foil and the leading end of the conductive paste filler, i.e., the printing surface, are arranged to form a continuous flat surface having the same height so that it is possible to apply a uniform pressure to the entirety of the multilayer wiring board assembly during thermocompression. It is therefore possible to fixedly laminate the multilayer wiring board assembly with a better electric connectivity.

Furthermore, since the adhesive layer is made of a thermosetting resin in accordance with the present invention, it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property with little damage to the respective boards during the manufacturing process.

Furthermore, the adhesive layer is formed of a thermoplastic resin to which is given a thermosetting property in accordance with the present invention, and therefore it is possible to manufacture a multilayer wiring board assembly having a good heat resisting property without damaging the conductive resin components (the conductive paste).

The foregoing description of the embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and obviously many modifications and variations are possible in light of the above teaching. The embodiment was chosen in order to explain most clearly the principles of the invention and its practical application thereby to enable others in the art to utilize most effectively the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 

What is claimed is:
 1. A multilayer wiring board assembly component comprising: a flexible resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste laterally extending beyond the perimeter of the opening of the through hole of the copper foil.
 2. The multilayer wiring board assembly component as claimed in claim 1 wherein said adhesive layer is made of a thermoplastic adhesive.
 3. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a flexible resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil, wherein the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with a copper foil or a conductive paste of an adjacent one of said multilayer wiring board assembly components.
 4. A multilayer wiring board assembly component comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film, and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil.
 5. The multilayer wiring board assembly component as claimed in claim 4 wherein said resin film is made of a flexible material.
 6. The multilayer wiring board assembly component as claimed in claim 4 wherein said resin film is made of a rigid material.
 7. The multilayer wiring board assembly component as claimed in claim 4 wherein said resin film is made of a rigid material.
 8. The multilayer wiring board assembly component as claimed in claim 4 wherein said resin film is made of a rigid material.
 9. The multilayer wiring board assembly component as claimed in claim 4 wherein said resin film is made of a rigid material.
 10. A multilayer wiring board assembly component comprising: a flexible resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and with a part of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of said copper foil.
 11. A multilayer wiring board assembly component comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and with a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil and being projected from said copper foil.
 12. The multilayer wiring board assembly component as claimed in claim 11 wherein said resin film is made of a flexible material.
 13. The multilayer wiring board assembly component as claimed in claim 11 wherein said resin film is made of a rigid material.
 14. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and with a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil and being projected from said copper foil, wherein the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with a copper foil or said conductive paste of an adjacent one of a multilayer wiring board assembly components.
 15. The multilayer wiring board assembly as claimed in claim 14 wherein said resin film is made of a flexible material.
 16. The multilayer wiring board assembly as claimed in claim 14 wherein said resin film is made of a rigid material.
 17. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and with a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through bole of the copper foil and being projected from said copper foil, wherein said multilayer wiring board assembly is laminated with a plurality of said multilayer wiring board assembly components through said adhesive layer in order that the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with said copper foil or a conductive paste of an adjacent one of a multilayer wiring board assembly components.
 18. A multilayer wiring board assembly component comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer made of a thermosetting resin and bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil.
 19. The multilayer wiring board assembly component as claimed in claim 18 wherein said resin film is made of a flexible material.
 20. The multilayer wiring board assembly component as claimed in claim 18 wherein said resin film is made of a rigid material.
 21. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer made of a thermosetting resin and bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil, wherein the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with a copper foil or said conductive paste of an adjacent one of a multilayer wiring board assembly components.
 22. The multilayer wiring board assembly as claimed in claim 21 wherein said resin film is made of a flexible material.
 23. The multilayer wiring board assembly as claimed in claim 21 wherein said resin film is made of a rigid material.
 24. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer made of a thermosetting resin and bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the through hole opening of the copper foil, wherein said multilayer wiring board assembly is laminated with a plurality of said multilayer wiring board assembly components through said adhesive layer in order that the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with said copper foil or a conductive paste of an adjacent one of a multilayer wiring board assembly components.
 25. A multilayer wiring board assembly component comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer made of a thermoplastic resin to which is given a thermosetting property and bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the through hole of the copper foil.
 26. The multilayer wiring board assembly component as claimed in claim 25 wherein said resin film is made of a flexible material.
 27. The multilayer wiring board assembly component as claimed in claim 25 wherein said resin film is made of a rigid material.
 28. A multilayer wiring board assembly laminated with a plurality of multilayer wiring board assembly components, at least one of said multilayer wiring board assembly components comprising: a resin film made of polyimide; a copper foil bonded to one surface of the resin film; an adhesive layer made of a thermoplastic resin to which is given a thermosetting property and bonded to the other surface of the resin film; a through hole opened through said copper foil, said resin film and said adhesive layer; and a conductive paste embedded in the through hole with a leading end of said conductive paste being projected outward from said adhesive layer and a tail end of said conductive paste being laterally extended beyond the perimeter of the opening of the copper foil, wherein the leading end of said conductive paste of said at least one of said multilayer wiring board assembly components makes electric contact with a copper foil or said conductive paste of an adjacent one of a multilayer wiring board assembly components.
 29. The manufacturing method of a multilayer wiring board assembly component as claimed in claim 14 wherein a separate paper is disposed in the outlet of said through hole near said adhesive layer in advance of said step of embedding said conductive paste.
 30. The manufacturing method of a multilayer wiring board assembly component as claimed in claim 18 wherein said adhesive layer is made of a thermosetting polyimide.
 31. The manufacturing method of a multilayer wiring board assembly as claimed in claim 24 wherein the conductive paste is finally cured at the same time as or after said multilayer wiring board assembly components are laminated together. 